IMO it is all about the conversion of the B preferreds
The higher the PPS, the less common shares for the B preferreds
Let's say the Ask looks like this:
2.89 <----- 1000 shares
2.25 <----- 3000 shares
2.20 <----- 1.9 million(!)
2.19 <----- 3000 shares
If someone wants to buy 3000 shares and sets a limited order to 2.19, he would get his 3000 shares for 2.19
Now the 2.19 is gone and the Ask looks like this:
2.89 <----- 1000 shares
2.25 <----- 3000 shares
2.20 <----- 1.9 million(!)
If someone wants to buy 50.000 shares and sets a 2.25 limit, the order should be executed at 2.20, because someone wants to sell 1.9 million shares at 2.20
The new Ask is
2.89 <----- 1000 shares
2.25 <----- 3000 shares
2.20 <----- 1.85 million(!)
As long as someone puts enough shares at the 2.20, he can create a "fake wall" there and prevent the PPS from rising.